Treating hydrocarbon fluids



Patented Feb. 16, 1943 TREATING HYDROCARBON FLUIDS John '1. Ward, Westfield, N. J., assignors to Gasoline Products Company, Inc., Newark, N. J., a

corporation of Delaware Application April 21, 1938, Serial No. 203,303

7 Claims.

This invention relates to methods of and apparatus for heating fluids, and refers in particular to methods and apparatus wherein hydrocar bon fluids are heated to a conversion temperature by passage through heater tubes or the like positioned within the radiant heating section of a furnace.

In the conversion of hydrocarbon-fluids it is general practice to heat the hydrocarbon fluids to a suitable conversion temperature in the radiant section of a furnace. Before any substantial amount of cracking or conversion of the hydrocarbon fluids occurs, the rate of transfer of heat to the heater tubes containing the hydrocarbon fluids may be xceedingly large Without the danger of coking. However, as the extent of conversion increases, it is necessary rapidly to decrease the rate of transfer of heat to the heater tubes and to the hydrocarbon fluids therein to avoid objectionable coking.

According to this invention a method of heating hydrocarbon fluids is provided whereby the hydrocarbon fluids are passed through heater tubes in the radiant or combustion section of a furnace, the heater tubes being disposed in a particular part of the radiant section so that the hydrocarbon fluids passing therethrough are sub jected to exceedingly high temperatures rapidly to raise the hydrocarbon fluids to a conversion temperature and initiate conversion thereof. After the conversion temperature isreached or after conversion has begun, the hydrocarbon fluids pass through heater tubes in the radiant or combustion section of the furnace which are disposed therein so that less heat is imparted to the hydrocarbon fluids and conversion thereof continues without objectionable coking.

The rate of transfer of heat to the hydrocarbon fluids in the heater tubes is controlled as contemplated by my invention by spacing the heater tubes, which may include floor, wall and roof tubes, with respect to each other or with respect to the boundary surfaces of the furnace. In one form of the invention the heater tubes are arranged in such manner that the distances between the heater tubes decrease in one direction or the distances from the wall or roof of the furnace decrease in one direction or both the distances between the tubes and the distances from the wall or roof decrease in one direction.

In a furnace having horizontally extending heater tubes arranged in a vertical row along the walls or boundary surfaces of the radiant or combustion section of the furnace, certain of the heater tubes in the hottest part of the furnace rapidly raised to a relatively high temperature,

whereas the wall tubes farther away from the hottest part of the furnace are positioned closer to each other or to the wall of the furnace so as to reduc and control the amount of heat to be farthest apart and farthest from the roof.

transferred to the hydrocarbon fluids in the heater tubes.

, When roof tubes are used, they may be arranged, for example, in a double row with the tubes adjacent the exit for the combustion gases from the radiant section being closest to each other and to the roof of the furnace while the roof tubes distant from the exit for the combustion gases from the radiant section are spaced In this way more heat is supplied to the roof tubes farthest from the combustion gas exit which are normally harder to heat. When two rows of roof tubes are used, the first row of roof tubes acts as a shield for the second row of roof tubes nearer the roof of the furnace and the latter row of tubes or a part thereof may be used as a soaking section.

The invention also contemplates apparatus suitable for controlled heating of hydrocarbon fluids.

The drawing represents a transverse vertical section of a furnace embodying one form of the invention, certain parts being diagrammatically shown to facilitate the disclosure.

Referring now to the drawing, the reference character l0 designates a furnace which is provided with a radiant heating section I 2 separated from a convection heating section I4 by a bridge wall it. The furnace shown is a box type furnace suitable for the pyrolytic treatment of hydrocarbon fluids but it is to be understood that this invention is not restricted thereto as the furnace may be of any desired shape or type adapted for the pyrolytic treatment of hydrocarbon fluids.

The radiant heating section is heated by hot products of combustion which are introduced into the radiant section in any desired manner, as, for example, by burners! extending through ports 20 in the end walls of the furnace. The: hot products of combustion pass from the radiant section over the bridge wall li into the convection section l4 and are withdrawn from the bottom of the section M by means of the duct 22 which may lead to a flue preheater or any other desired apparatus, not shown, and then to the atmosphere.

A plurality of tubes 25 is positioned in the path of the hot combustion gases sweeping through the convection section l4 and the tubes are heated by the heat contained in such gases. The tubes 2d may be arranged within the convection section in any desired manner and may comprise a single bank or a plurality of banks of tubes interconnected in any desired sequence for the flow of fluids therethrough in a single stream or in plural streams. As shown in the drawing, the tubes are arranged in staggered relation and are interconnected for the flow of a single stream of hydrocarbon fluid or the like therethrough in a direction countercurrent to the passage of hot combustion gases through the convection section.

In the heating of hydrocarbon fluids to conversion temperatures it is desirable to bring the hydrocarbon fluids to a relatively high temperature as rapidly as possible to raise the hydrocarbon fluids to a conversion temperature. After conversion starts and as the rate of conversion increases, the rate of heat transfer to the hydrocarbon fluids is decreased to avoid objectionable coke deposition in the heater tubes. The method'ofheating the hydrocarbon fluids and the arrangement of the heater tubes in the radiant section 12 of the furnace herein set forth form part of the invention whereby the desired heating of the hydrocarbon fluids is obtained.

A plurality of sets of heater tubes is contained in the radiant heating section l2 of the furnace l9 and these tubes are arranged along the walls or other boundary surfaces of the radiant section so as to be substantially out of the path of the hot. products of combustion sweeping through such section and are heated predominantly by radiant heat. A row of tubes 26 is arranged vertically along the bridge wall l6 and another row of tubes 28 is arranged. vertically along the side wall of the furnace opposite the bridge wall [6. These tubes 26 and 28' are connected by lines 35 and32jshown diagrammatically for conveying the hydrocarbon fluids being heated from row 28 to row 26 and then back to row 23, etc. I have shown tubes on only two of the vertical boundary surfaces of the section l2 for simplicity, but in practice I prefer to place similar tubes on the other two vertical boundary surfaces thus providing a coil with tubes thereof on all four vertical walls, that is, front, back, side and bridge walls. Two rows of tubes 34 and 35 are preferably arranged in staggered relation along the roof of the radiant section l2 of the furnace. The arrangements shown are for the purpose of illustration and it Will be evident that the invention can be practiced with any desired arrangement where it is desired to control the rate of transfer of heat to selected heater tubes. The radiant heating section l2 may also be provided with one or more rows of floor tubes which may be arranged to control the transfer of heat thereto. Also single or plural rows of tubes may be employed in the vertical banks 26, 28 of tubes described.

The novel arrangement of the tubes will now be more specifically described to more clearly set forth how the rate of heat transfer to the respective sets of heater tubes and the rate of heat transfer to the hydrocarbon fluids passing Gil therein depends on the distance of the heater tube from the source of radiant heat, the direct radiation from the source of radiant heat and also the secondary radiation or reradiation from the walls or boundary surfaces of the radiant section of the furnace.

By increasing the distances between the heater tubes adjacent the hottest part of the radiant section, more heat is radiated to such heater tubes. By increasing the distances between such heater tubes and the walls or boundary surfaces of the radiant section of the furnace, the walls or boundary surfaces receive more heat and the amount of heat radiated to the heater tubes from the Walls of the radiant section of the furnace is increased. By decreasing such spacing of the tubes from each other or from the walls of the radiant section, the opposite effect is obtained and the rate of heat transfer is decreased. It is thus apparent that the rate of transfer to the various heater tubes of a given row of heater tubes may be controlled by changing the spacing between the heater tubes and the spacing between such heater tubes and the adjacent walls or boundary surfaces of the furnace, or by changing the spacing between the heater tubes or the spacing between such heater tubes and the adjacent walls or boundary surfaces of the furnace.

In the drawing there is shown one embodiment for practicing the invention where the hottest zone in the radiant section l2 will normally be in the neighborhood of the burners I8 but it is to be understood that the hottest zone of the radiant section may be at a higher or lower elevation. The furnace shown in the drawing is for purposes of illustration only and it is to be understood that box type furnaces may be operated to have the hottest zone in the region of the roof section nearest the bridge wall I6 and when using my invention. in such furnaces, the heater tubes will be so arranged with respect to the boundary surfaces of the furnace and with respect to each other that the heating of the hydrocarbon fluids passing through the tubes will be regulated or controlled as desired. However, the burners may be so positioned and operated that there is substantially complete combustion in the lower portion of the furnace or already formed hot products of combustion are introduced at such point so that the hottest part of the furnace will be in the lower portion withresultant greater heat input to the tubes in closest proximity to the burners or to the point where hot combustion products are introduced into the furnace. If the furnace is so operated that the hottest zone is near the top of the bridge wall IS, the roof tubes may be omitted, or they may be so arranged that the correct amount, of heat input is given to the roof tubes and the flow of the hydrocarbon fluids through the roof tubes may be changed so that the hydrocarbon fluids passing therethrough receive the correct amount and consequently to the hydrocarbon fluids of heat. The drawing, merely shows one form of apparatus which may be usedrto practice my invention but one skilled in the art will be, able to clearly apply the principles of my invention to other furnaces in accordance. with the, disclosure herein set forth.

Hydrocarbon fluids such as an oil to be treated are passed through line 40 by pump 42 and are preheated by being passed through heater tubes 24 in the convection section M of the furnace W. The preheated hydrocarbon. fluids are then passed through line to the lowest horizontally arranged heater tube 46 of the row 28 in the radiant section [2. The hydrocarbon fluids are then passed through line 36 to the lowest horizontally arranged heater tube 68 of the row 26 of tubes adjacent the bridge wall l6 and then through line 32 to the heater tube 56 of the row 28 of tubes adjacent the side wall of the radiant section l2. The flow of the hydrocarbon fluids continues from a tube in row 28 to a tube in row 26 and the heated hydrocarbon fluids pass from top tube 5| in row 26 to top tube 52 in row 26 and are then passed through the roof tubes 34 and 36 as will be later described in more detail.

The hydrocarbon fluids in passing through the banks or rows of tubes 26 and 28 are rapidly raised to a conversion temperature. In order to obtain a maximum transfer of heat to the lower heater tubes of rows 26 and 28 and to the hydrocarbon fluids passing therethrough, the tubes are spaced at greater distances'from each other and the walls in the hottest part of the radiant section l2, as at 53, 54, 56 and 56 than they are near the upper ends of the rows 26 and 28 of the heater tubes as at 60, 62, 64 and 66.

In this way the lowermost tubes are subjected to more direct radiation and also due to the increased spacing of the lowermost tubes, the walls or boundary surfaces as at 68 and 16 receive more direct radiant heat and are heated to a relatively high temperature. These hot walls reradiate heat to the parts of the tubes which are not exposed to direct radiation from the source of radiant heat to more uniformly heat the hydrocarbon fluids passing through the tubes. By spacing the tubes in this manner the heater tubes are heated quickly and uniformly and the hydrocarbon fluids passing therethrough are raised to a conversion temperature.

After conversion of the hydrocarbon fluids has begun, it is desirable to increase the ex-- tent of cracking as the hydrocarbon fluids pass through the heater tubes but care must be exercised to avoid excessive heat input as otherwise objectionable coking occurs. To provide for the desired heat input the heater tubes are spaced closer together at the upper portions of the rows 26 and 28, as at 66, 62, 64 and 66, to reduce the amount of heat passing to the heater tubes and the walls behind them. In addition the heater tubes at the upper portions of the rows 26 and 23 may be spaced closer to the side wall and bridge wall l6 of the furnace to reduce the amount of heat reradiated from such side wall and bridge wall. In the embodiment of the invention illustrated in the drawing it will be seen that the spacing between consecutive heater tubes in the rows 26 and 28 progressively decreases in passing from the bottom towards the top of the furnace l and that the spacing between the consecutive heater tubes in the row 26 and bridge wall I6 and the spacing between the consecutive tubes in row 28 and the side wall of the furnace l0 progressively decrease in the same direction. But I am not to be restricted thereto as certain sections of the heater tubes may be uniformly spaced at greater distances apart than other sections of the heater tubes.

The heated hydrocarbon fluids leave the rows 26 and 28 of the' heater tubes at a conversion temperature and are passed through roof tubes comprising the lower row 34, through connection 12 and thesecond or upper row 36 where additional heat is imparted to the fluids to increase the conversion rate and provide for the desired soaking. The products of conversion then pass through line 14 and may be further treated to separate hydrocarbons having the desired boiling range as is well known in the art.

When roof tubes are used, they may also be so arranged and spaced to control the amount of heat transferred thereto. The roof tubes are preferably staggered and the tubes 15 and 16 of row 36 and tubes 11 and 18 of row 36 distant from the bridge wall 16 are preferably spaced from each other at greater intervals than the tubes 86 and 8| of row 34 and tubes 82 and 83 of row 36 adjacent the top of the bridge wall l6 as shown in the drawing to control the rate of heating of the hydrocarbon fluids passing through the roof tubes. The second row 36 of roof tubes is shown substantially parallel to the first row 36 of the roof tubes to control the heat input thereto but this arrangement is not essential. The hot products of combustion passing over the bridge wall l6 to the flue exit heat that portion of the furnace ill to a greater extent than the upper left hand portion 96 of the furnace near tubes 15 and 16, and by spacing the tubes as shown, the amount of heat being transferred to the roof tubes may be controlled. The row of tubes 36 receives less heat input than the row 34 and may be used as a soaking section for the hydrocarbon fluid. Where no roof tubes are used, other provisions for a soaking section may be made.

In the embodiment of the invention shown in the drawing the spacing between the consecutive roof tubes in rows 34 and 36 progressively decreases in a direction from left to right as viewed in the drawing and the spacing between consecutive tubes in each of these rows and the roof decreases in the same direction but other arrangements are contemplated whereby the rate of heat transfer to the heater tubes is controlled,

The following table is given by way of example to show the effect upon rate of heat transfer by changing the spacing between heater tubes of a given row. The table includes values for tubes arranged in both single rows and in double staggered rows.

Single row 4 O. D Spacing C-O 7 7 I6; I FA Heat density 10,00 I?! Til [X Ififjf 5 O. D. Spacing C-0 8% 10 11% l3" l4 Heat density. H 9, 630 10, 590 11, 280 11, 900 12, 530

Double row staggered i O. D. Spacing 0-0 7% 9 10 12 13% Heat densityl First row 7, 930 8, 500 9, 080 9, 575 10, 040 D0 Second row 3, 030 4, 460 5, 660 6, 725 7, 460

5 O. D. Spacing 0-0 8% 10 11% 13 14% Heat density First row VVVVV 7, 770 8, 050 8, 600 8, 975 9, 470 Do .1 Second row 2, 510 3,590 4, 680 5, 585 6, 430

In the above table, C-C means center to a center; Heat density means the rate of heat transfer or B. t. 11. per hour per square foot; and O. D. means-outside diameter of the heater tubes.

The above table merely illustrates the relative absorption of radiant heat by tubes having .different spacing between each other. The figures given are merely illustrative and may be varied depending upon the particular furnace under consideration. For example, higher heat input may be employed in the hottest part of the furnace, the higher heat input being in some instances up to 25,000 or 30,000 B. t. u. per hour per square foot.

From the above table it will be seen that with a substantially constant source of radiant heat, the amount of heat transferred to the tubes may be varied by varying the spacing between the tubes. From the above table it will also be seen that when tubes are arranged in two rows along a boundary surface of a radiant heating section of a furnace, the rate of heat transfer to all heater tubes is decreased below the value which the. respective tubes would receive if similarly ar-' ranged in a single row. This result is obtained even though the heater tubes in the respective rows are arranged in staggered relationship.

The heater tubes as illustrated in the embodiment shown in the drawing are so arranged to obtain a decreasing rate of heat transfer as the degree of cracking increases. In accordance with one form of my invention hydrocarbon fluid to be treated are passed upwardly through the consecutive heater tubes in the rows 26 and 28 and the rate of transfer of heat to such hydrocarbon fluids will decrease, the rate of transfer being greatest adjacent the burners Hi, the hottest part of the furnace. If the hydrocarbon fluids are then passed from the heater tubes in I'OWs 28 and 28 through the lower row 34 and upper row 36 of roof tubes in the direction from left to right as viewed in the drawing, the rate of heat transfer will continue to decrease.

A Mid-Continent gas oil to be cracked having a gravity of 30 A. P, I. is subjected to a superatmospheric pressure of about 200 to 1000 pounds per square inch and is maintained under uperatmospheric pressure during; the cracking treatment. The gas oil is heated to about 725 to 825 F., preferably about 775 F., in the preheater tubes 24 in the convection section. The preheated gas oil is then further heated by being passed through the lower tubes 46 4B and 50 in the rows 25 and 28; of the heater tubes in the radiant section where the heat density or heat input is about 22,000 B. t. u. per hour per square foot. Cracking of the gas oil is begun during passage of the oil through these lower tubes. In some cases a heat density or heat input of 25,000 to about 30,000 B. t. u. per hour per square foot may be used.

When the heated gas oil reaches the middle tubes 92 and 94 in the rows 26 and 28, it is at a temperature of about 850 F. and the heat density or heat input has been decreased to about 20,000 B. t. u, per hour per square foot while the conversion to gasoline is about 2%. The heat input to wall heater tubes decreases as the oil passes upwardly through the upper tubes to tubes 5| and 52. The heated gas oil at a temperature of about 930 F. i then passed into the end roof tube'15 and through the lower row of roof tubes 34 where further heat is added. The heat input at the inlet of the lower row of roof tubes has been decreased to about 15,000 B. t. u. per hour per square foot and the conversion to gasoline has increased to 7%.

.At the outlet-end (tube 8|) of the lower row of roof tubes 35 the oil is at a temperature of about 1000 F. and the heat input has decreaset to about 10,000 B. t. u. per hour per square foot while the conversion to gasoline ha increased to about 16%. The oil is then passed through the upper row 35 of roof tubes and leaves the furnace through line 14 at a temperature of about 1000 F. The heat input at the outlet end (tube 8|) of the upper row of roof tubes has been decreased to about 8000 B. t. u. per hour per square foot while the conversion to gasoline of the oil during its passage through the upper row of roof tubes has increased to about 35%.

I am not to be restricted to the above example which is given by way of illustration only, as different conditions may be used for different stocks and for different treatments, it only being necessary so to space the tubes as to control the amount of heat transferred to the heater tubes in different sections of the furnace. For example, temperatures up to 1500 F., and pressures from atmospheric to 5000 pounds per square inch may be used.

While the invention has been described in connection with the conversion of hydrocarbon fluids, it is to be understood that the invention may be used for heating hydrocarbon fluids generally where it i desired to control the rate of heat transfer to the hydrocarbon fluids.

Floor tubes may be used instead of or in addition to the wall tubes. Further, the invention may be used on all types of furnaces to obtain the results above set forth. Also, different flows of hydrocarbon fluids may be used with the heater tubes in order to apply mOst heat to the hydrocarbon fluids passing through the heater tubes where it is desired.

From the foregoing it will be seen that my invention provides for heating hydrocarbon fluids at different rates while being passed through heater tubes positioned in the radiant section of the furnace by controlling the rate of heat transfer to the heater tubes. I have found that this can be accomplished by varying the spacing between heater tubes and by varying the spacing between heater tubes and the boundary surfaces of the furnace and while I have shown a particular arrangement in the drawing, it is to be understood that this is merely by way of example and different arrangements of the heater tubes for controlling heat input to the heater tubes are within the contemplation of my invention.

I claim:

1. A heating apparatus adapted for heating hydrocarbon fluids to conversion temperature including a heating chamber, means for supplying heat to said heating chamber, a row of spaced horizontally extending heater tubes arranged along; a boundary surface of said heating chamber, certain of said heater tubes being spaced at greater distances from each other'and from said boundary surface than the rest of the heater tubes in said row;

2. A heatingapparatus adapted for heating hydrocarbon fluids to conversion temperature including a radiant heating section and a convection section separated by a bridge wall, a plurality of spaced heater tubes arranged along a wall and along said bridge wall in said radiant heating section, and adapted to convey hydrocarbon, fluids to be heated, means for supplying heat to said heater tubes, certain of said heater, tubes in each row being spaced at greater distances from each other and from the wall and bridge wall, respectively, than other tubes in such rows of said radiant heating section whereby more heat is transferred to the heater tubes more widely spaced and further from the wall and bridge wall, respectively, of said radiant heating section.

3. A heating apparatus adapted for heating fluids including a heating chamber, means for supplying heat to said heating chamber, a row of spaced heater tubes arranged along a boundary surface of said heating chamber, said heater tubes near one end of the row being spaced at greater distances from each other and from said boundary surface than said heater tubes near the other end of said row.

4. A heating apparatus adapted for heating fluids including a heating chamber, means for supplying heat to said heating chamber, a row of spaced heater tubes arranged along a boundary surface of said heating chamber, said heater tubes being adapted to convey fluids to be heated and being spaced so that the distances between said heater tubes decrease progressively from one end of the row of tubes to the other. e

5. A heating apparatus adapted for heating fluids comprising a heating chamber, means for supplying radiant heat to said heating chamber, a row of spaced heater tubes disposed along a boundary surface of said heating chamber to receive radiant heat, with certain of said heater tubes of said row being spaced at greater distances from each other and from said boundary surface than others of said row whereby more heat is reradiated from said boundary surface to certain of the tubes of said row than to others of said row.

6. A heating apparatus adapted for heating fluids comprising a heating chamber, means for supplying radiant heat to said chamber, a row of spaced heater tubes disposed along a boundary surface of said heating chamber to receive radiant heat, with the heater tubes disposed along one section of said boundary surface being spaced at greater distances from the boundary surface and from each other than the tubes disposed along another section thereof, whereby certain of said tubes are subjected to more radiant heat .than others.

'7. A heating apparatus adapted for heating fluids comprising a heating chamber, means for supplying radiant heat to said heating chamber, a row of spaced heater tubes disposed along a boundary surface of said heating chamber to receive radiant heat, said tubes being spaced so that the distances between the heater tubes and the distances between the heater tubes and the boundary surface decrease progressively from one end of the row of tubes to the other.

JOHN T. WARD. 

